Count business days excluding holidays

Q: Count business days excluding holidays

This is a Coding & Algorithms interview question from Airtable for Software Engineer roles. View the full question and solution on PracHub.

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Question

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Problem: Count Working Days Between Two Dates

Given a start date, an end date (inclusive), and a set of holiday dates, compute the number of working days.

A working day is a date that:

is not Saturday or Sunday, and
is not in the provided holiday set.

Input

startDate : string in YYYY-MM-DD
endDate : string in YYYY-MM-DD (guaranteed endDate >= startDate )
holidays : list of distinct date strings in YYYY-MM-DD

Output

An integer: number of working days in [startDate, endDate] .

Example

startDate = 2026-12-24
endDate = 2026-12-28
holidays = [2026-12-25]

Dates:

12/24 Thu (work)
12/25 Fri (holiday, not work)
12/26 Sat (weekend)
12/27 Sun (weekend)
12/28 Mon (work)

Output: 2

Constraints (typical)

Date range length up to $10^6$ days for a naive iteration; design an approach appropriate to the stated constraints.
Holiday count up to $10^5$ .